Gripping gasket

ABSTRACT

A novel gasket includes at least one gripping element embedded in an annular member for forming a seal between two tubulars. For tubulars having socket and spigot ends, the gripping element includes teeth for gripping an outer surface of the spigot end and a blunt tooth for contacting a front wall of the socket end. The blunt tooth rolls along the front wall during relative movement between the tubulars and can include a contacting face of a specialized geometry to adjust contact dynamics and/or roughened surfaces to increase the frictional contact between the blunt tooth and the front wall. The embedded element can also include at least four teeth arranged such that no more than two teeth normally grip the outer surface of the spigot end. One or more teeth can also include a transverse groove to enhance penetration into the outer surface of the spigot end.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/817,674, filed Apr. 2, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to devices for locking joints for tubularmembers. More particularly, the present invention relates to gaskets forsealing and locking a socket end of one tubular to a spigot end ofanother tubular.

2. Description of the Prior Art

Pipes joined in telescoping relationship typically have a spigot end ofone pipe inserted into the socket end of the engaging pipe. The socketend has an opening large enough to receive the spigot end of theenclosed pipe. A gasket is inserted in the socket end of the enclosingpipe and prevents leakage of fluid from the joint by forming a sealbetween the two pipes. In many applications, a fluid under pressureflows through the pipes. This fluid pressure can produce a separatingforce, known as joint separating end thrust, that can cause the pipes toseparate at the joint.

One method of locking the joint between two pipes involves configuringas sealing gasket as a restraining mechanism. For example, a resilientsealing gasket can be provided with a number of circumferentially spacedapart metal inserts. These metal inserts include teeth that are adaptedto penetrate an outer surface of a pipe spigot end. Upon installation,the teeth bite into the pipe spigot end to prevent the pipe spigot endfrom sliding out of the socket end. As is known, the dimensions of thepipe spigot and socket ends, while conforming to industry standards, canvary during manufacture. The ability of the gasket to seal and lock thejoint, however, can be adversely affected by such dimensionalvariations. Thus, there is a persistent need for sealing and restraininggaskets that can accommodate pipes having such dimensional variations.Moreover, there is a persistent need for gaskets that lock or retain ajoint without unduly compromising the structure of the pipe (e.g.,excessive penetration). The present invention addresses these and otherneeds of the prior art.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a retention and sealingdevice for joints between tubulars. In one embodiment, the device isused to join a first tubular having a socket end with a second tubularhaving a spigot end. The exemplary device includes a resilient annularmember having a sealing portion for forming a seal between the firsttubular and the second tubular and at least one gripping elementembedded in the resilient member. The gripping element, which is formedof a relatively hard material, includes a plurality of teeth projectingradially inward relative to the socket for gripping an outer surface ofthe spigot end and a blunt tooth extending axially forward relative tothe socket for contacting a front wall of the socket. The blunt toothadapted to contact and roll along the front wall during relativemovement between the first and second tubulars. The terms radiallyinward(ly) and radially outward(ly) are used with reference to the axialcenterline of the tubulars (i.e., meaning pointing toward or away fromthe tubular centerline, respectively). The terms axially forward refersto a direction toward the end of the tubular and term axially rearwardrefers to a direction toward the middle of the tubular.

In certain embodiments, the blunt tooth can include features andelements for enhancing the rolling contact between the blunt tooth andthe front wall of the socket end. For instance, the blunt tooth can havea contacting face of a specialized geometry (e.g. convex, concave, flat,etc.) to selectively adjust the location of initial contact, contactpressure, or other parameter (e.g., contact dynamics). Additionally, aroughened surface on the blunt tooth can be used to increase thefrictional contact between the blunt tooth and the front wall. Suitableroughness can be obtained by using an irregular surface formed by gritblasting, chemical etches, spline protrusions, knurled protrusions,impregnated grit, composite constructions, bonded elements, and coatedelements.

In embodiments, the embedded element can also include arrangements toenhance the locking function provided by the gripping elements,facilitate assembly, improve product life and improve performance, etc.For instance, the embedded element can include least four teeth arrangedsuch that no more than two teeth grip the outer surface of the spigotend when the spigot end is inserted into the socket end. For instance,at least three can lie along a common arc. Additionally, the embeddedelement can include a ridge extending radially outwardly from theembedded element to limit the movement of the blunt tooth along thefront face. In certain embodiments, at least one tooth includes atransverse groove that enhances the tooth's ability to penetrate intothe outer surface of the spigot.

It should be understood that examples of the more important features ofthe invention have been summarized rather broadly in order that detaileddescription thereof that follows may be better understood, and in orderthat the contributions to the art may be appreciated. There are, ofcourse, additional features of the invention that will be describedhereinafter and which will form the subject of the claims appendedhereto.

BRIEF DESCRIPTION OF THE DRAWING

Other objects and advantages of the present invention will becomeapparent to those skilled in the art from the following description ofthe invention taken in conjunction with the accompanying drawing inwhich like numerals indicate like elements and in which:

FIG. 1 illustrates a cross-sectional view of a jointed between anenclosing pipe and a mating pipe that uses a gasket made in accordancewith one embodiment of the present invention;

FIG. 2 illustrates an end view of a gasket made in accordance with oneembodiment of the present invention;

FIG. 3 illustrates a methodology for arranging inwardly projecting teethaccording to one embodiment of the present invention;

FIG. 4 illustrates the motion of a gasket insert made in accordance withone embodiment of the present invention during use; and

FIG. 5 illustrates an isometric view of a gasket insert made inaccordance with one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to devices and methods providing ruggedand cost-effective gasket arrangements for pipe joints. The presentinvention is susceptible to embodiments of different forms. There areshown in the drawings, and herein will be described in detail, specificembodiments of the present invention with the understanding that thepresent disclosure is to be considered an exemplification of theprinciples of the invention, and is not intended to limit the inventionto that illustrated and described herein. As used herein, the termsradially inward(ly) and radially outward(ly) are used with reference tothe axial centerline of the tubulars (i.e., meaning pointing toward oraway from the tubular centerline). The terms axially forward means in adirection toward the end of the tubular and term axially rearward meansin a direction toward the middle of the tubular. Further, no particulargeometry, material, or other technical limitation is implied by the term“gasket.” Rather, as used herein, this term merely refers to a devicefor providing at least a seal at a discontinuity in a flow path of afluid.

Referring now to FIG. 1, there is shown a joint formed by a firstenclosing pipe 10 having a bell end 12 and second pipe 14 having aspigot end 16. To make up a joint, the second pipe 14 is pushed into thebell end 12 of the enclosing pipe 10. Conventionally, the inner surfaceof pipe bell end 12 has a retainer groove 18 bounded by a front wall 20,a retainer wall 22, a circumferential compression rib 24 that projectsradially inwardly from a sealing wall 26, and a throat portion 28 thatterminates at the front wall 20. Moreover, the inner surface can alsoinclude a shoulder 30 formed adjacent the retainer wall 22.

A gasket 50 made in accordance with one embodiment of the presentinvention locks together the pipes 10 and 14 and also provides a fluidseal at the joint. As will become apparent, the gasket 50 includeselements and features that co-act with the pipes 10 and 14 in a mannerthat preserves the integrity of the joint by accommodating relativemotion between the pipes 10 and 14.

Referring now to FIGS. 1 and 2, in one embodiment the gasket 50 includesa resilient body 51 provided with a plurality of relatively hardsegments 52. The segments 52, which can be formed of a suitable metal,are circumferentially arrayed in a spaced-apart fashion within the bodyof the gasket 50. In one embodiment, the segments 52 are firmlyvulcanized into radial grooves in gasket 50. The segment 52 can also beembedded into the gasket by bonding, encapsulation, over-molding,mechanical cooperation, or by one of many other suitable methods. Thenumber of segments 52 inserted into the gasket 50 can vary dependingupon the anticipated fluid pressure at the joint and the size of thepipes involved. The segments 52 can be suitably machined, investmentcast, extruded, forged, or by other suitable manufacturing methods. Thesegment 52 can include one or more features for enhancing the integrityof the joint between pipes 10 and 14. While the features are describedbelow as being provided on one segment 52, it should be understood thateach feature can be utilized separately as well as in conjunction withone another.

In one embodiment, the segment 52 has three teeth 54, 56 and 58 pointedradially inwardly such that the teeth 54, 56 and 58 can bite into anouter surface of the spigot end 16 when the spigot end 16 is insertedinto the pipe bell end 12. The segment 52 can include a fourth tooth 60also adapted to bite into the outer surface of the spigot end 16. Theteeth 54-60 can be equally spaced or asymmetrically spaced relative toone another. Merely for convenience, the three teeth 54, 56 and 58 willbe referred to as rearwardly positioned and the fourth tooth 60 will bereferred to as forwardly positioned. In one embodiment, the forwardtooth 60 will be located “inside” a circle described by the common arc Aof the three rearward teeth 54-58. It is believed that positioning theforward tooth 60 “inside” the boundary of the common arc, or relatively“removed” away from the spigot 16, can reduce the insertion forcerequired to assemble the joint. It will be appreciated that when aplurality of teeth are arranged along a common arc, only two teeth cancontact a flat surface at any given time (of course, excluding factorssuch as teeth penetration and deformation). In some embodiments, morethan four teeth can be used. In such embodiments, each subsequentforwardly positioned tooth would also be located inside the common arcof the rearwardly positioned teeth such that each subsequent forwardtooth would be more removed from the spigot than the preceding tooth.

Referring now to FIG. 3, another method of defining the relativepositioning of four (or more) teeth 54-60 is to consider orienting thesegment 52 such that a line can be drawn between the two middle teeth56,58. A declination angle d of the forward tooth 60 is “greater” than adeclination angle e of the rearward tooth 58. For instance, the angle ofdeclination e for the rearward tooth 58 can be defined as at least 3degrees but less than 10 degrees while the forward angle of declinationd would be greater than 10 degrees but no more than about 15 degrees.Subsequent teeth rearward and/or forward would be aligned in compliancewith the angles of declination defined above.

The segment 52 can also include a nose 64 projecting generally axiallytoward the wall 20. The nose 64 has a blunt end 66 configured to engagethe wall 20. In particular, the blunt end 66 is constructed as toprimarily roll on the wall 20 as opposed to biting into or sliding onthe wall 20. Rolling friction between the blunt end 66 and the wall 20can be enhanced by roughening the surface of the blunt end 66, such asby providing knurls 68 on the blunt end 66. Other methods of rougheninginclude grit blasting, chemical etching, spline protrusions, gritimpregnation, composite constructions, bonded or coated elements, etc.

Referring now to FIGS. 1 and 4, during use, the hydraulic pressure ofthe fluid flowing in the pipes 10 and 14 can create a thrust force thatcan cause the joints to separate (joint separating end thrust). Whenpresent, the joint separating end thrust will cause the blunt nose 66 tocontact the front wall 20. Once joint separating end thrust initiatescontact between the blunt face and the front wall 20, the frictionalinterference forces are relatively static, as long as the jointseparating end thrust is maintained in a static state. Frictional forcestransition from static to dynamic rotational rolling forces as thesegment 52 rotates (generally shown with arrow B) in response toincreasing joint separating end thrust. Typically, the nose 66 of thesegment 52 will have a defined contact surface area C1 with the frontwall 20. Continued increasing joint separating end thrust will result inthe rotation of the segment 52 as shown with arrow B. Each increment ofrotation on the part of the segment 52 will result in a change in thecontact surfaces between the front wall 20 and blunt nose 66. Anincremental rotation is shown with segment 52A in phantom lines with anassociated new contact point C2. Contact point C2 now acts as a newfulcrum or pivot point for rotation as shown by arrow B′. Thus, as thesegment 52 rotates, the contact surface areas of the blunt nose 66 andthe front wall 20 continually changes. Each additional increment ofrotation will establish yet a new set of contact surfaces and pivotpoints between the blunt nose 66 and the front wall 20.

The segment 52 can also include a ridge 70 that operates as a mechanicalstop to prevent excessive movement of the segment 52 during cases ofextreme variations in the dimensions of the pipes 10 and 14. The bluntridge 70 projects radially further outward than the nose 64 and ensuresthat the contact point between the blunt nose 60 and the front wall 20does not migrate in such a way as to contact the most radially outwardsurface 72 of the socket or pipe bell end 12. The blunt ridge 70includes resilient encapsulation 74 that provides a cushion between theblunt ridge 70 and the most radially outward surface 72 of the socket orpipe bell end 12—should they come in contact with each other. Theencapsulation 74 may be confined to intermittent areas over segment52—or be continuous around gasket OD.

In some embodiments, one or more recesses can be provided in the segment52 to accommodate material than deforms upon the application of theforces and pressures inherent during use. For example, a recess orpocket 76 is provided between the blunt ridge 70 and the blunt nose 64.The recessed pocket 76 can be continuous or intermittent at the bluntridge 70. In one embodiment, the volume of the recess 76 isapproximately equal to the volume of the blunt ridge 70. This volumetricrelationship between ridge 70 and the recess 76 gives the encapsulation72 covering the blunt ridge 70 a place to flow into during contact—aform of void volume fill. It should be understood that fractionalrelationship between the volumes of the ridge 70 and the recess 76 canalso be suitable in many applications. In any case, this recessed pocket76 provides an element of flexibility and/or adjustment due to minorpipe shifting, surging, hammer, et cetera.

Also, the segment 52 further includes a scallop 78 formed on an outerrearward surface 79. Conventionally the gasket body 51 can include asealing or bulb portion 53 that provides a fluid barrier between thepipe 10 and second pipe 14. For instance, the bulb portion 53 forms aseal between the inner wall 26 of the pipe 10 and the outer surface ofthe spigot end 16. The scallop 78, as will be discussed in greaterdetail below, can reduce the compressive forces on the bulb portion 53and thereby reduce the risk that the bulb portion 53 bursts or otherwisefails during use.

The gasket 50 can also include a groove 77 formed on an outercircumferential diameter adjacent the ridge 70. The groove 77 is adaptedto receive the shoulder 30 of the pipe bell end 12. The groove 68 issized such that the gasket 50 can pivot at least partially around theshoulder 30 when the spigot end 16 is moving into or out of pipe bellend 12.

Referring now to FIGS. 1 and 5, there is isometrically shown anothersegment 80 made in accordance with one embodiment with the presentinvention. The segment 80 includes a plurality of teeth 82, 84, 86 and88 and a blunt nose 90. As described earlier, the teeth 82-88 extendradially inward toward the spigot 16. The teeth 82-88 include at leastone groove 92 passing through each tooth 82-88. The groove 92 istransversely oriented relative to the radially inward extending teeth82-88. By splitting the teeth 82-88, the groove 92 provides a focusedcontact point between the teeth 82-88 and the spigot 16. The focusedcontact points allow teeth to penetrate faster and deeper into thespigot or other mating surface for any set of conditions as comparedconvention teeth that have a more distributed loading of pressure. Thegroove can be constructed from many geometric forms includinghalf-round, dovetailed, trapezoid, square, rectangular, etc. The groove92 also provides a haven for swaged and displaced material as teeth82-88 bite into the spigot 16, which allows the teeth 82-88 to allowenhanced penetration. Likewise, the blunt face 90 also includes at leastone groove 96 that is transversely oriented relative to the axiallyextending blunt face 90. The groove 94 splits the blunt face 90 andprovides a focused contact point between the blunt face 90 and the frontwall 20. The focused contact point provides increased frictionalinterference forces by focusing contact loads over a smaller surfacearea. The groove 94 can be constructed from many geometric formsincluding half-round, dovetailed, trapezoid, square, rectangular, etc.This will focus the biting penetration and provide deeper and fasterpenetration.

In still other embodiments, the nose can be formed as an acutely pointedtooth having at least one face or the other or both faces defining thetooth to be non-linear surfaces instead of a flat surface. The purposeof at least one non-linear surface defining the faces of the toothresults in a deeper and/or faster bite penetration of the tooth into thefront wall 20 for any given set of parameters. Moreover, it should alsobe appreciated that the groove can be applied to a tooth designed tobite into the front wall 20. Non-linear surfaces include various convexand/or concave combinations. Non-linear surfaces include groundsurfaces, hollow grounding, and various other methods of achievingarcuate convex and/or concave surfaces defining the tooth. Adjusting thegeometry of the blunt nose 66 can adjust the contact points between theblunt face, adjust contact pressure, and other behavior characteristics.It should be appreciated, therefore, that the contact dynamics betweenthe blunt nose 66 and the front wall 20 can be adjusted (e.g., optimizedor otherwise controlled) by altering the geometry of the blunt nose 66.

Referring now to FIG. 1, during installation, the gasket 50 is fittedinto the pipe end 12 of the enclosing pipe 10. The second pipe 14 isthen inserted into the pipe end 12. As the spigot end 16 of the secondpipe 14 enters the gasket 50, one or more of the teeth 54, 56 and 58contact the outer surface of the spigot end 16. The forwardly positionedtooth 69 (if present) is recessed and, therefore, does not impede themovement of the spigot end 16 into the pipe 10. As the spigot end 16engages the teeth 54, 56 and 58, the segment 52 rotates about theshoulder 30 such that the bulb portion 53 is squeezed between the innersurface 26 and the segment surface 79. Advantageously, the scallop 78minimizes the stresses imposed on the gasket 50 during insertion. Unduestress on the gasket during insertion can result in unnecessarilyelevated insertion force—and may dislodge the gasket. The recessedscallop reduces insertion force by reducing stress introduced to thegasket—thus reducing incidence of dislodgment and/or displacement ofgasket during assembly. Further, the rotation of the segment 52 cancause one or more of the rearward teeth to disengage from the spigot end16 and the forward tooth 60 to engage the spigot end 16. Thus, it shouldbe appreciated that the segment 52 can be constructed such that aselected or predetermined number of teeth can be made to engage thespigot end 16 regardless of the rotational orientation of the segment52. Once the second pipe is fully inserted into the enclosing pipe 10,installation or joint make up is substantially complete.

As noted earlier, during use or operation, the hydraulic pressure of thefluid flowing through the joint can produce joint separating end thrustthat can cause the spigot end 16 to slide out of the pipe 10. Thissliding action causes one or more of the teeth 54-60 to bite orpenetrate into the spigot end 16. As noted earlier, the particular teeththat have engaged the spigot end 16 can depend on the rotationalorientation of the segment 52. Thus, the sliding motion of the spigotend 16 draws the gasket 52 axially outward until the blunt nose 66engages the front wall 20. The blunt 66, upon engaging the front wall20, allows the segment 52 to rotate in a controlled manner and alsomodulates the radial movement of the segment 52. Also, the blunt ridge70 engages the surface 72 during excessive radial movement of thesegment 52 and thereby prevents the blunt nose 66 from riding up to thesurface 72.

While the invention has been described in the environment of a pipejoint in which the bell end of the enclosing pipe has a compression rib24, the gasket will also perform its sealing function with a bellconfiguration such as that shown in U.S. Pat. No. 2,953,398 which doesnot have a compression rib. Further, it should be understood that theteachings of the present invention can be also applied to mechanicaljoints other than those utilizing socket-spigot ends such as for exampleflanged joints. That is, the present invention may be utilized in anymechanical arrangement wherein the relative movement of two tubulars (orother fluid conduits) can compromise a fluid seal there between.Further, whereas the present invention has been described with respectto specific embodiments thereof, it should be understood that theinvention is not limited thereto as many modifications thereof may bemade. It is, therefore, contemplated to cover by the present applicationany and all such modifications as fall within the true spirit and scopeof the appended claims.

1. A device for joining a first tubular having a socket end with a second tubular having a spigot end, the socket end having a retainer groove formed by a front wall, a radially outward surface, a retainer wall, and a circumferential compression rib that projects radially inward from a sealing wall, the device comprising: (a) a resilient annular member having a sealing portion for forming a seal between the first tubular and the second tubular: (b) at least one gripping element positioned in the resilient member, the gripping element having: (i) a plurality of teeth projecting radially inward toward the spigot end for gripping an outer surface of the spigot end; and (ii) a blunt tooth extending axially forward toward the socket end for contacting the front wall, the blunt tooth rolling along the front wall during relative movement between the first and second tubular.
 2. The device of claim 1 wherein the blunt tooth includes one of (i) a convex face, and (ii) a concave face.
 3. A device for joining a first tubular having a socket end with a second tubular having a spigot end, comprising: (a) a resilient annular member having a sealing portion for forming a seal between the first tubular and the second tubular; (b) at least one gripping element positioned in the resilient member, the gripping element having: (i) a plurality of teeth projecting radially inward toward the spigot end for gripping an outer surface of the spigot end; and (ii) a blunt tooth extending axially forward toward the socket end for contacting a front wall of the socket, the blunt tooth contacting and rolling along the front wall during relative movement between the first and second tubular, wherein the blunt tooth includes a roughened surface for increasing the frictional contact between the blunt tooth and the front wall.
 4. The device of claim 3 wherein the roughened surface includes one of: (i) an irregular surface formed by grit blasting, (ii) chemical etches, (iii) spline protrusions, (iv) knurled protrusions, (v) impregnated grit, (vi) composite constructions, (vii) bonded elements, and (viii) coated elements.
 5. The device of claim 3 wherein the plurality of teeth includes at least four teeth arranged such that no more than two teeth grip the outer surface of the spigot end when the spigot end is inserted into the socket end.
 6. The device of claim 5 wherein at least three of the at least four teeth lie along a common arc.
 7. The device of claim 3 wherein the gripping element includes a ridge extending radially outward from the gripping element, the ridge positioned to limit the movement of the blunt tooth along the front wall.
 8. A method for joining a first tubular having a socket end with a second tubular having a spigot end, the socket end having a retainer groove formed by a front wall, a radially outward surface, a retainer wall, and a circumferential compression rib that projects radially inward from a sealing wall, the method comprising: (a) forming a seal between the first tubular and the second tubular with at least a portion of a resilient annular member; (b) positioning at least one gripping element in the resilient member, the gripping element having a plurality of teeth projecting radially inward toward the spigot end for gripping an outer surface of the spigot end, and a blunt tooth extending axially forward toward the socket end for contacting the front wall, the blunt tooth rolling along the front wall during relative movement between the first and second tubular.
 9. A method for joining a first tubular having a socket end with a second tubular having a spigot end, comprising: (a) forming a seal between the first tubular and the second tubular with at least a portion of a resilient annular member; (b) positioning at least one gripping element in the resilient member, the gripping element having a plurality of teeth projecting radially inward toward the spigot end for gripping an outer surface of the spigot end, and a blunt tooth extending axially forward toward the socket end for contacting a front wall of the socket end, the blunt tooth contacting and rolling along the front wall during relative movement between the first and second tubular; and (c) roughening a surface of the blunt tooth to increase the frictional contact between the blunt tooth and the front wall.
 10. The method of claim 9 further comprising arranging at least four teeth of the plurality of teeth such that no more than two teeth grip the outer surface of the spigot end when the spigot end is inserted into the socket end.
 11. The method of claim 9 further comprising limiting the movement of the blunt tooth along the front wall using a ridge formed on the gripping element.
 12. A gasket for mating a first pipe having a socket end with a second pipe having a spigot end, the socket end having a retainer groove formed by a front wall, a radially outward surface, a retainer wall, and a circumferential compression rib that projects radially inward from a sealing wall, the device comprising: (a) an annular body formed of a resilient material, the annular body having a central opening allowing the spigot end to enter therethrough; (b) a plurality of inserts positioned in the annular body, each insert having: (i) a plurality of teeth projecting radially inward toward the spigot end for gripping an outer surface of the spigot end; and (ii) a blunt tooth extending axially forward toward the socket end for contacting the front wall, the blunt tooth rolling along the front wall during relative movement between the first and second tubular.
 13. A gasket for mating a first pipe having a socket end with a second pipe having a spigot end, comprising: (a) an annular body formed of a resilient material, the annular body having a central opening allowing the spigot end to enter therethrough; (b) a plurality of inserts embedded in the annular body, each insert having: (i) a plurality of teeth projecting radially inward toward the spigot end for gripping an outer surface of the spigot end; and (ii) a blunt tooth extending axially forward toward the socket end for contacting a front wall of the socket, the blunt tooth rolling along the front wall during relative movement between the first and second tubular, wherein the blunt tooth includes a roughened surface for increasing the frictional contact between the blunt tooth and the front wall.
 14. The gasket according to claim 13 wherein the roughened surface includes one of: (i) an irregular surface formed by grit blasting, (ii) chemical etches, (iii) spline protrusions, (iv) knurled protrusions, (v) impregnated grit, (vi) composite constructions, (vii) bonded elements, and (viii) coated elements.
 15. The gasket according to claim 13 wherein the plurality of teeth includes at least four teeth arranged such that no more than two teeth grip the outer surface of the spigot end when the spigot end is inserted into the socket end.
 16. The gasket according to claim 15 wherein the plurality of teeth includes at least four teeth and wherein at least three of the at least four teeth lie along a common arc.
 17. The gasket according to claim 13 wherein the plurality of inserts each include a ridge extending radially outward therefrom, the ridge positioned to limit the movement of the blunt tooth along the front wall.
 18. The gasket according to claim 17 wherein the plurality of inserts includes a resilient encapsulation for providing a cushion between the ridge and a surface of the socket end. 